1. Field of the Invention
The present invention relates to a material having a surface possessing antifouling activity, particularly excellent antifouling activity against greasy stains or soils and a process for producing the same, and a coating composition for the antifouling material and an apparatus for the production process.
2. Background Art
Conventional methods for making the surface of materials antifouling comprises smoothening the surface to physically make it difficult for stains or soils to be deposited on the surface. In other methods, excellent oxidative degradation activity of a photocatalyst fixed onto the surface is utilized to degrade organic matter or stains or soils deposited on the surface are washed away by utilizing superhydrophilification of a photocatalyst. In these methods, however, satisfactory antifouling properties may not be enough when greasy stains or soils are badly deposited or when light is not enough to develop the photocatalytic activity cannot be obtained.
The following materials are known wherein an inorganic layer is formed on the surface thereof so as to associate with or so as not to associate with antifouling properties of the surface.
Japanese Patent Laid-Open No.98324/1978 discloses a method which comprises coating a colloidal silica-based inorganic coating onto a porous inorganic substrate to form an undercoat, coating an alkali silicate-based inorganic coating thereon to form a top coat, and then curing the coatings at room temperature or by heating to impart heat resistance and other properties to the substrate.
Japanese Patent Laid-Open No.123639/1993 discloses a method which comprises applying a synthetic resin coating as an undercoat onto the surface of a porous substrate, such as calcium silicate, applying an inorganic coating as an intermediate coat onto the undercoat, and then applying an inorganic coating composed mainly of an alkali metal silicate onto the surface of the intermediate coat.
Japanese Patent Laid-Open No.278431/1997 discloses a hydrophilic film wherein the center line average roughness Raxe2x80x2 on the surface of the film is 0.5 to 500 nm and the surface is composed mainly of concaves and convexes with the repetition length of concaves and convexes in plane direction of the surface being not more than 0.5 xcexcm.
Japanese Patent Laid-Open No.227160/1997 discloses a photocatalytically hydrophilic member having a layer containing a photocatalytically active titanium oxide and an amorphous oxide.
Japanese Patent Laid-Open No.9995/1994 discloses a stain or soil removing method using a water-soluble alkali metal salt. This method is characterized in that a soil or stain release agent containing a water-soluble alkali metal silicate is coated onto stains or soils deposited onto the surface of the substrate to include the stains or soils in the soil or stain release agent and, thereafter, the soil or stain release agent containing the stains or soils are removed, thus removing the stains or soils. Since this soil or stain release agent is not fixed onto the substrate, the stain or soil removing method is merely a temporary soil or stain removing method like that using a surfactant-containing detergent.
None of the above prior art methods, however, disclose that the incorporation of satisfactory amounts of an alkali metal and non-bridging oxygen in an amorphous metal oxide can offer excellent antifouling properties and abrasion resistance.
Accordingly, it is an object of the present invention to provide an antifouling material, which, independently of environment, such as indoor or outdoor environment, can semi-permanently exhibit excellent surface antifouling properties, particularly excellent antifouling activity against greasy stains or soils and, in addition, is resistant to abrasion. It is also an object of the present invention to provide a process for producing the same, and a coating composition and apparatus for the antifouling material and the production process.
The present invention has been made with a view to attaining the above object. According to a first aspect of the present invention, there is provided an antifouling material comprising: a substrate; and an inorganic layer consisting essentially of an amorphous metal oxide, said inorganic layer containing an alkali metal and non-bridging oxygen in an amount effective to remove contaminants, derived from an exhaust gas, adhered on the surface of the inorganic layer with running water alone to restore the diffuse reflectance of the surface of the inorganic layer to not less than 75% of the initial diffuse reflectance, said inorganic layer being fixed as the outermost layer of the antifouling material.
According to a second aspect of the present invention, there is provided a coating composition for the formation of an antifouling inorganic layer on the surface of a substrate in the production of the antifouling material, said coating composition comprising: a solvent; and a solute, the solute comprising at least one member selected from the group consisting of an alkali silicate, an alkali aluminate, an alkali zirconate, an alkali borate, an alkali phosphate, and an alkali phosphonate.
According to a third aspect of the present invention, there is provided a process for producing an antifouling material, comprising the steps of: applying the coating composition onto the surface of a substrate to form a coating; and heating the substrate to fix the coating of the coating composition as an antifouling inorganic layer on the surface of the substrate.
According to a fourth aspect of the present invention, there is provided an apparatus for producing an antifouling material, said apparatus comprising coating means for applying the coating composition to form a coating onto the surface of a substrate; and heating means for rapidly heating the substrate to fix the coating of the coating composition as an antifouling inorganic layer onto the surface of the substrate.